A mesh member, namely a filter, used in rectification assembled in a flow pipe, has been conventionally known. The mesh member is produced by exerting a plastic working, such as drawing-machining, on a net body to forma dome shape, the center of which projects so as not to interfere with a vane in the pipe. The shape of the mesh member before processing is shown in FIG. 3. A net body 100 having side portions 100b, 100b . . . constituting a plurality of through holes 100a in a shape of lattice is formed on a metal plate and is drawn into a dome shape, thereby obtaining the mesh member.
In this case, there arises a problem that stress caused by expansion force generated at the time of drawing-machining is applied to the thin linear side portions 100b, 100b . . . and the side portions 100b are easily broken. Such a problem may be prevented by reducing speed of pressing at the time of drawing-machining and gradually molding the mesh member by a series of press processes; however, such solutions are not efficient.
In Patent Literature 1, a porous portion is formed on a metal plate and is heated by baking by a heating apparatus such as a burner, thereafter the metal plate is pressed with a desirable press mold. Patent Literature 1 discloses that the porous portion is unlikely to be broken by the press process because the porous portion is heated by baking before being pressed.